1. Field of the Invention
The present invention relates to toner for electrostatic charge development used for copy machines and printers practically applying electrographic technology, and an image forming method using the same.
2. Description of the Related Art
In conventional electrographic methods, a latent electrostatic image formed by charging and exposing a photoconductor surface is developed by colored toners to form a toner image, the toner image is transferred onto a member to be transferred such as transfer paper and this is fixed with a heat roll to form an image.
In a dry development system employed in the electrographs and electrostatic recordings, a system using a two-component developer composed of the toner and a carrier and a system using a one-component developer containing no carrier are available. In the former system, the good images are obtained relatively stably, but the images with constant quality are hardly obtained over a long time because the carrier is easily deteriorated and variation in a mixed ratio of the toner and the carrier occurs easily, and there are also drawbacks in maintenance and downsizing of the apparatus. Thus, the latter system using the one-component developer which does not have such drawbacks has been noticed.
In this system, a procedure in which the toner (developer) is fed by typically at lest one toner feeding member, and the latent electrostatic image formed on a latent image bearing member is visualized by the fed toner is employed. At that time, it has been described that a layer thickness of the toner fed on the surface of the toner feeding member must be thin as possible. In particular, when the one-component developer is used and its toner has high electrical resistance, it is necessary to charge this toner by a developing device. Thus, the layer thickness of the toner must be remarkably thin. Because if this toner layer is thick, only the vicinity of the surface of the toner layer is charged and the entire toner layer is hardly charged uniformly.
In the right of such requests, various procedures (toner layer thickness regulating procedure) to regulate the layer thickness of the toner on the toner feeding member have been proposed, and as a representative, one which controls the layer thickness of the toner by using a pressing member (regulating blade), counterposing this regulating blade to the toner feeding member thereby pressing the toner fed on the toner feeding member surface with the regulating blade is available. A type which obtains the same effect by abutting a roller in place of the blade is also available.
In a developing step, it is necessary to control a charge amount of the toner in a proper range in the toner layer formed on a developing roller surface by the toner layer thickness regulating member. When the charge amount is low, a binding force to the developing roller becomes weak, spout from a developing device and recovery defect to the developing device occur, scattering of the toner and leakage of the toner easily occur. Such phenomena easily occur in a late phase of durability or under a high temperature and high humidity environment.
In order to solve such problems, various treating agents are used as described later, but various problems occur. In magnesium silicate minerals (attapulgite, sepiolite) described in Japanese Patent Application laid-Open (JP-A) No. 2002-31913, a percent of water content is high, charge defect easily occurs even in the ordinary use environment, and problems such as scumming, toner leakage, and toner scattering caused by the charge defect occur easily.
When magnesium silicate treated with silicone oil described in JP-A No. 03-294864, JP-A No. 04-214568 and JP-A No. 05-165257, due to the silicone oil, fluidity of the toner is deteriorated and charge increase is caused, feeding defect and density reduction are caused in the developing device. Magnesium silicate having particle diameters described in Examples is easily dissociated in the developing device, a developing member and the latent image bearing member are easily stained. Particularly in the toner using an organic boron compound, the durability is remarkably deteriorated and the image is harmfully affected.
In the toner described in JP-A No. 11-95480, when the toner is made by using magnesium silicate as a silicate fine powder body and making a coated rate 60% to 100%, if used as a negatively charged toner, a reversely charged toner occurs easily and the scumming is easily caused. Because magnesium silicate easily has the positive charge by the effect of an MgO moiety which easily has the strongly positive charge as shown in the relation with electronegativity (Journal of the Imaging Society of Japan, 39: No. 3:259).
As the toner described in JP-A No. 11-184239, when a titanic acid fine powder body is used, this material itself is low resistant, thus, the leakage of charge is large, the scumming, the toner leakage and the toner scattering occur easily.
As the toner described in JP-A No. 2003-186240, when titania is used, this material itself is low resistant and highly conductive. Thus, it is difficult to control an amount to be added, when added in a large amount, the charge leakage is large and the charge reduction of the entire toner is caused. when added in a small amount, the charge increase is caused. Thus, in both cases, the scumming, the toner leakage and the toner scattering occur easily.